c
...@supra.com (
Clay Cowgill) wrote:
~ In article <32DA9A24.3
...@magenta.com>, j
...@magenta.com wrote:
~
~ > Second, to correct the X-deflection output. Space Duel, Gravitar and
~ > Tempest all used Wells-Gardner
~ > monitors, while the dedicated
Major Havoc game used the amplifone. Im
~ > not sure of the exact reason
~ > but the Wells-Gardner monitors have a pincusion effect on a linear
~ > input. Because of this there was
~ > corrective circuitry on the game PCB's of SD,G and T. These are
~ > analog multipliers that correct for
~ > this non-linearity. Since
Major Havoc used the Amplifone, none of the
~ > analog multipliers were needed.
~ > No big deal, but if you run a
Major Havoc game PCB on a Wells-Garner
~ > monitor you will have some pincusioning(arched in top and bottom,
~ > looking at a drawn square box, such as self test). The adapter
~ > board contain the necessary circuitry to remedy this. But to tell you
~ > the truth, when the game playing
~ > it is hard to see any effect from this pincushioning.
~ >
~ > Any additions
Clay??
~
~ Nope. Well put. ;-) I'm not sure if the Ampliphone has the correction in
~ the yolk response or on the deflection board somehow.
By extending the neck of the CRT, Amplifone lowered the distance_to_center to
distance_to_outside ratio allowing for less of a bowing effect, they then glued
little magnetic strips of metal to strategic spots on the yoke's perimeter to
help linearize the display.
~ It looks like
~ Cinematronics might have solved it by using a smaller section of the
~ "sweep" developed by the analog integrators, although they also have some
~ funky analog stuff in there as well.
Cinematronics used a diode/resistor ladder in the feedback of their integrators
to compensate for the yokes greater effect on the outside edges of the CRT.
Using the a smaller section of the "sweep" allowed them to draw straight lines
*anywhere* on the screen. Since the charging of a capacitor in an integrator is
non-linear, they chose the most linear section of the charge curve to be used as
the "vector".
~ I guess Atari used more expensive
~ caps to try to get a more linear charge curve.
Perhaps, but that's not the reason for "bowing", this is caused by the yoke's
greater effect, on the CRT beam on the outside edges of the CRT. This is
because of the longer distances traveled by the electrons as they flow from the
CRT guns, to the outside edges of the CRT, as opposed to the center of the CRT.
The greater distances give more time, for the yoke, to effect the path of the
electrons. You end up with bowing, and if not corrected for, the images
displayed will grow in size as they approach the edges of the CRT.
Atari chose multipliers to correct for the bow, and VDRs to correct for the
image growth and ended up with the nicest picture of the lot. (IMHO)
~
~ At any rate, the WG monitor will "bow" as Jess describes unless a
~ correction board is used. I've got a breadboard version of the correction
~ board working (mostly) in my garage, but I've yet to produce any PCB's for
~ it...
I look forward to it!
-Zonn
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